Electric spark gap



11 9 c. L. M. .LE

ELECTRIC SPARK GAP 12 :1 Fig. 2 .v-Filed April 18 1923 Pay. .5

Patented Jan. 11, 1927.

UNITED STATES 1,613,709 PATENT OFFICE.

CHARLES LEONARD ARMANI) MAURICE LEBLAnc, or PARIS, FRANCE, ASSIGNOR T0 SOCIE'IE ANONYME POUR LEXPLOITATION nns PRooEnEs MAURICE LEBLANC- VICK'ERS, OF PARIS, FRANCE.

ELE CTRIC SPARK GAP.

' Application filed. April 18, 1923, Serial No. 632,928, and in France April 22, 1922.

The subject of the present invention is an electric spark-gap which is constructed in such a way as to have the following properties, which any good spark-gap should possess as far as possible.

Firstly. It should function like an electric valve and allow only currents having a given direction to pass. One ofits two electrodes oughtto be able to act only as anode and the other only as cathode ,'shown diagrammatically by two spheres in Fig. 1.

Secondly. So long as the gap is not broken down, no current should be able to pass from the anode to the cathode.

Thirdly. It ought to break down when the potentialdifference set up between the electrodes reaches a value H generally high.

but which ought to be fixed very accurately.-

An arc jumps from the anode to the cathode and the potential difference maintained between them ought to drop at the same instant to a very low amount with respect to the value H, whatever may be the strength of current which passes by the arc. In other Words, matters ought tohappen as if the two electrodes were short-circuited.

Fourthly. If the strength of current passing by the arc drops to zero, for example, by tending to change its sign, the spark-gap ought at once to become dead and oppose the passage of any current from its anode to its cathode until it has again been started to spark over by re-establishing the potential difference H between them.

Fig. 1 is a diagrammatic view of an ordinary spark-gap. Fig. 2 is a similar view of a spark-gap constructed in accordance with one embodiment of this invention. Fig. 3 is a similar view of a different arrangement. Fig. 4 is a sectional View of the grid element. Fig. 5 is a diagrammatic view illustrating an arrangement for converting a direct current into an alternating current of high frequency. Fig. 6 is a similar view showing an arrangement of elements for rectifying an alternating current of any desired frequency for producing the required bias on the grid. Fig. 7 illustrates the'curve of an electric oscillation which may be produced by the arrangement shown in Fig. 5; and, Fig. 8 is a diagrammatic View showing the method :of operating several receivers in parallel.

The spark-gap forming the subject of the present invention consists of a vacuum tube A, Fig. 2, which contains:

1. An iron or carbon anode a,

2. A mercury cathode Z),

3. An auxiliary anode a located immediately adjacent to the cathode. A local source of electricity, for example a small battery of accumulators, is connected across them and supplies an auxiliary are which keeps a part of the surface of the mercury in a continuous state of incandescence,

4. A grid 0 which fills the Whole section of the tube and is located between the anode a and the auxiliary anode a. It is connected externally to the anode a by a circuit which includes-another local source of electricity giving a constant electromotive force H, and which is inserted in the circuit in such a way as to keep the grid at a potential lower by the amount H than that of the anode a. w i

The tube A constitutes an electric valve, through which currents can only pass by going from the anode a to the cathode b. The first of the requirements is thus satisfied.

If we suppose the cathode to be at zero potential, and if the anode is also at this same potential, the grid will have a potential H. So long as this last is not brought up to incandescence, its permeability by the electrons is very small, and no current of appreciable strength can reach it, by using it as cathode. By way of precaution a very high resistance may be given to the circuit which connects it to the anode 0;.

The grid is therefore negatively charged with respect to the cathode .7).

If the potential of the anode increases and becomes h, the potential of the grid becomes h-H. As long as h is smaller than H the grid continues to be negatively charged with respect to the cathode, and drives back the electrons which tend to issue from it. No current can pass from the anode a to the cathode Z), and the second of the above mentioned requirements is satisfied.

But when the potential 71, becomes equal to H, the grid is at the same potential as the cathode, and takes no further charge with respect to it. The electrons then issue from the cathode to go to the anode; the sparkgap breaks down.

Since it is the work of the agitated atoms of the incandescent cathode, which sets free the electrons, very small drops in potential, chiefly localized at the surface of the electrodes, are suflicient to make the current pass, whatever its strength may be.

Atthis time the potential of the grid again becomes much less than that of the cathode, but so long as the current passes, positive ions pass through the grid in going from the anode to the cathode. The grid attracts some of them to itself until its charge becomes annulled by them. It neutralizes many of them as of the electrons which it can emit, but can emit only a very small number of these with respect to the number emitted by the incandescent cathode, and consequently with respect to the number of positive ions which pass through it.

In these conditions all its bars become surrounded by veritable sheaths of positive ions and its total charge remains Zero. The action of the grid is thus done away with so long as the current )asses, and this latter passes through the tube as if the grid did not exist. The third requirement is thus sat isfied.

But if the potential drops to zero, the current is interrupted, and at the same time the stream of positive ions through the grid. Generally speaking the potential h after having dropped to zero, wi l be negative during a certain time. How the number of positive ions e veloping the grid will always be very small, and an exceedingly short time will be sufi'icient for it to net alize them. From this instant the grid will have regained a negative charge with respect to the cathode and the spark-gap becomes dead. The fourth requirement is satisfied.

The spark-go.

which is the subject of this invention presents the following great advantages:

l. The potential ll for break-down depends neither on the distance nor on the state of the surface of the electrodes nor on the pressure of the mercury vapour which fills the tube. it is fixed by the electromotive force which causes the potential difference H and which it is easy to make constant.

2. The cathode kept artificially incandescent is clearly distinguished from the anode. The tube behaves like an electric valve and the current of necessity ceases when the potential changes sign.

3. The passage of the current does not affect the electrodes.

But it is necessary that the sparking potential of the tube A should be higher than the potential H. Therefore if this latter is very high, it is preferable to make the tube A. long, provided that it be bent back on itself as shown in Fig. 3.

The grid must be located in proximity to the cathode in order that it may the more easily prevent the emission of the electrons.

It is suiiicient if it is prevented from itself becoming a cathode, and for this purpose if it is prevented from heating, as for example by making its bars highly conductive and by soldering their ends to a metal cylinder having a large radiating surface as shown in Figs. 3 and a, and further by giving a very high resistance to the circuit which connects it with the anode in such way as to limit the current which mi 'ht be established through it to a few milli-amperes.

When the sparking potential H is very high, it is inconvenient to use batteries or accumulators to charge the grid. The charge is effected by means of an alternating-current of any frequency stepped up to the de sired voltage by a small transformer and then rectified.

By way of example the arrangement shown in Fig. 6 may be used.

The transformer is provided with two identical secondary circuits 1 and 2, the point of entrance of the former is connected to the anode of a valve 8, and the point of exit of the latter to the anode of a valve 4. The point of exit of the circuit 1 and the point of entry of the circuit 2 are connected to the return conductor of the system.

The two cathodes of the valves are connected to the grid 5 through an induction coil 6. Finally in order to ensure the constancy of the grid potential two condensers 'Z' and 8 are inserted between the return conductor of the system and the two ends of the induction coil.

It was assumed in Fig. 2 that the cathode was kept incandescent by a small set of accumulators. In most cases it will be advantageous to use two auxiliary anodes, and to cause them to produce fixed arcs by the passage of alternating-currents of any like frequency but out of phase. It has also been assumed that the cathode consisted of a globule of mercury because then it reconstitutes itself without help. But it may also be made of a metal filament kept in a state of incandescence. In other words, the tube, which is the subject of this invention may be replaced by a three electrode lamp, such as de Forests, previously filled with argon for example, and in which the exhaustion has not been carried to the extreme limit, so that the current which passes through it may be carried by ions and not by electrons.

One of the principal applications of this spark-gap is the production of sustained waves or the conversion of a direct-current supplied from a source at constant strength into alternating-currents with a frequency generally high and with constant strength or constant voltage.

In the arrangement shown in Fig. 5 the source of direct-current at constant strength is shown at E. The current which it supplies passes first through an induction coil 13, which will ensure almost absolutely the iZil constancy of the current during the duration of the eriod of the alternating-current which it is esired to produce. There are inserted in shunt between the point of exit of this induction coil and the return conductor, firstly, the spar -gap A together with its accessories, secondly, a circuit containing a resonator consisting of the condenser C and the induction coil D, then the working circuit or primary circuit F of a transformer, the secondary circuit of which supplies the working circuit U, as shown in the figure.

To make the apparatus work, the sparkgap A is short-circuited, until the direct-current supplied from the source E has reached its normal strength I. The shortcircuit is then interrupted, the current passes into the resonator and the action of the coil, B very quickly brings it up to the strength I which remains constant thereafter. The condenser is charged and the potential of the anode of the spark-gap is increased.

During this time, the strength I being kept constant, all the electromotive'forces of self-induction in the coil D and the primary circuit F, if it exists, are zero. The potential difference it applied to the spark-gap may be taken as equal to that applied to the condenser C.

lVhen it becomes equal to H, the gap breaks down and becomes practically a shortcircuit which is traversed by the current of constant strength I supplied by the source E. At the same time an oscillatory discharge current is started in the closed circuit through the resonator C D and the spark gap A and is superposed in the latter on the constant current I supplied by the source; the strength i and the potential difference h of the oscillatory current vary as shown by the curves 2' and h in Fig. 7.

The strength 2' decreases from the point M where it has the value I, passes through a.

minimum, and at the point P regains its initial value I; at this instant therefore the current in the spark-gap ceases, the latter stops working, and the coil B keeps the strength constant and equal to I in the resonator. The condenser is recharged. The point A on the curve of potentials it corresponds to the point P; from this point A onwards the potential difference at the terminals of the condenser increases, the more quickly as the current I is stronger, and is represented appreciably by the straight line A B. At the point B, it regains. the value H, and the spark-gap again breaks down; the strength 2' then changes according to the curve Q R S, and the phenomenon already described is repeated and so on in succession. The curve of current strength i in the resonator circuit has therefore the shape M N P Q R S T.

The curves of current strength and of voltage will be deformed to a smaller extent the greater is the energy stored in the resonator with respect to that expended in the apparatus and in the working circuit during the duration of the period of the alternatingcurrent produced. In this manner an alternating-current of constant strength is obtained.

If it is wished to operate several receivers 9, 10, 11, etc. by'currents of constant voltage, they may be connected in parallel between the conductors leading from the terminals of the. secondary circuit G of the transformer, the primary circuit F of which is connected in series with the resonator (Fig. 8). Provided that all the circuits 9, 1O, 11, etc, and G are fitted with condensers which convert them into resonators tuned to the same frequency as the first, a constant potential difference will be applied to them.

What I claim is: V

1. An apparatus for the conversion of continuous current into alternating current, including a source of continuous current, an electric circuit connected thereto, a selfinduction coil in series in said circuit, a resonator in series in said circuit, an electric spark-gap in shunt upon the supply circuit of said resonator and including a three-electrode tube in which the current is conveyed by ions, an auxiliary source of current for maintaining the cathode of said tube in a state of incandescence, a circuit connecting the grid and anode of said tube and provided with a source of constant elec-tromotive force for maintaining said grid negative with respect to said anode.

2. An apparatus for the conversion of continuous current into alternating current, including a source of continuous current, an

electric circuit having a self-induction coil and a condenser in series, a second self-induction coil connected thereto, a spark-gap in shunt with the supply circuit of said resonator and including a three-electrode tube in which the current is conveyed by ions, a circuit having a source of constant electromotive force connecting the grid and anode of said spark-gap'so that said grid is maintained. negative with reference to said anode and the grid-cathode circuit is closed after traversing said resonator.

3. An apparatus for the conversion of continuous current into alterating current, including a source of continuous current, an electric circuit including a self-induction coil and a condenser in series and having a second-self induction coil connected thereto, a sparlcgap comprising a three-electrode tube in which the current is conveyed by ions associated with said circuit, a circuit having a source of constant electric-motive force connecting said grid and anode of said tube for maintaining said grid negative with reference to said anode so that the grid-cathode circuit will be closed after traversing said resonator and a transformer primary in series in said resonator circuit and adapted to collect the alternating cu rent produced.

l. An apparatus "for the conversion of continuous current into continuous electric oscillations, including a source of continuous current, an electric circuit having a self-induction coil and a condenser in series and provided with a second self-induction coil connected thereto, a spark-gap in shunt with the supply circuit of said resonator and including a three-electrode tube in which the current is conveyed by ions, circuit provided with a source of constant electro-rnotive force connecting the grid and anode of said spark-gap for maintaining said grid negative with relation to said anode so that the gridcathode circuit will be closed after traversing said resonator.

5. An apparatus for the conversion of continuous current into electric oscillations including a source of continuous current, an electric ciruit connected thereto, a self-induction element in series in said circuit, a resonator in series with said element, a spark-gap in shunt across the supply circuit of said A resonator and including a three electrode bulb whereby the current is conveyed by ions, an auxiliary source of current for maintaining the cathode of said bulb in state of incandescence, a circuit connecting the grid with the anode of said bulb and provided with a source oi constant eletroinotive force so as to maintain said grid negative relatively to said anode and a transformer primary in series with said resonator circuit for receiving the electric oscillations produced.

In testimony whereof I have signed this specification.

CHARLES LEONARD ARMANI) MAURICE LEBLANC. 

